Technologists and designers for internal combustion engines implement various technologies and control strategies to improve engine characteristics such as fuel efficiency. Electronic throttle control is a technology that has been broadly implemented on internal combustion engines for passenger vehicles. Electronic throttle control offers opportunities for engine control, previously unavailable, that may be exploited to improve fuel economy. Improvements in engine characteristics through use of electronic throttle control strategies may benefit any engines employing throttles, including conventional spark-ignition engines, some compression-ignition engines, and engines that employ intermediate engine control strategies, such as homogeneous-charge compression-ignition engines.
One opportunity for improving fuel economy and managing engine operation comprises vehicle coasting, wherein input commands to the vehicle indicate that the operator has no need for braking or acceleration of the vehicle. Under such circumstances, there may be gains to fuel economy if the vehicle is able to sustain vehicle momentum during the coasting event. Prior systems to take advantage of vehicle momentum during coasting include transmission design and controls, such as optimization of torque converter designs and transmission control methods to decouple the engine from the driveline. Other systems have increased air flow through the engine by increasing engine idle control settings, to reduce engine pumping losses. Idle control systems are limited in their ability to improve engine breathing during coast down events, due to their limited authority to control air into the engine. What is needed is a method and system to improve engine performance during coast down events by improving engine breathing and reducing pumping losses, thus improving engine efficiency and fuel economy.